Production of non-porous vacuum metallized coatings on strip material



g- 1965 R. M. BRICK PRODUCTION OF NON-POROUS VACUUM METALLIZED COATINGSON STRIP MATERIAL Filed June 1, 1960 mmmnm Wm w mm g 120M; M Bria/z INVEN TOR United States Patent 3,197,861 PRODUCTION OF N 0N-POROUS VACUUMMETAL LIZED CGATINGS 0N STRIP MATERIAL Robert M. Brick, Hinsdale, Ill.,assignor to Continental Can Company, Inc, New York, N.Y., a corporationof New York Filed June 1, 1960, Ser. No. 33,267 16 Claims. (Cl. 29-528)This invention relates in general to new and useful improvements instock having metal coatings thereon and the method of forming the same,and more particularly relates to the production of non-porous metallizedcoatings on strip material.

Metallic coatings employed for the prevention of corrosion arepractically always somewhat porous when applied as thin coatings. Forexample, every automobile owner is familiar with rusting of theso-called chrome decorative trim which is in reality steel covered by anickel electroplate and a superficial thin chrome plate. Theelectroplated chrome is always porous and is used only for a brightfinish. The nickel is to prevent rusting by excluding oxygen and watervapor. However, when the nickel coating is too thin, rusting will occurby reason of pores in the electroplated nickel. The same is true ofelectroplated tin coatings on steel.

Tin plate normally used for the manufacture of cans is a so-called A:lb. coating, nominally 0.000015 inch thick, is very porous and the steelwill rust through this coating in a few days when exposed to highhumidity and warm air. After the tin plate is brightened by fusion ofthe tin, many of the pores are closed up, but enough of the pores remainopen to show rusting after exposure to warm humid atmospheres in a fewweeks.

The porosity of thin metallic coatings is not limited to those obtainedby electroplating. Vacuum deposited coatings, gas plated coatings (i.e.,from metal carbonyl or halide gases which decompose on hot metal todeposit a coating), sputtered coatings, etc., all exhibit porosity whenthe coatings are thin. For example, a vacuum metallized coating of0.000015 inch thickness of aluminum on steel, equivalent in thickness toA lb. electroplated tin, also shows relatively rapid rusting in warmhumid air and coating thicknesses of at least 0.000030 inch are requiredto duplicate or improve upon 4 lb. fused electro-tin plate.

It is, of course, desirable to retain the metal coating as thin aspossible in order to effect a saving of both time and money.Accordingly, it is an object of the invention to close the pores ofnewly metal coated strips by rolling the coated strips to effect a flowof the metal of the coating and a resultant permanent closing of thepores through the welding together of the metal as it flows together.

It has been found that if the metallized coating is exposed to theatmosphere, the oxide which immediately forms will prevent the properwelding shut of the open pores even if the metal coated strips arepassed through rolls which apply pressures on the metal coatings toeffect the'llowing thereof. The pores are partially closed mechanicallybut apparently oxygen and water vapor molecules can still move throughthe pores to cause rusting of the steel substrate, for example. On theother hand, when metallic surfaces are free of oxides or chemisorbedoxygen and thus in a nascent state, pressure bonding or welding is veryeasily accomplished by bringing the atoms of two such surfaces togetherto normal interatomic distances for the metal concerned, i.e., about2(l0) cm., at normal iuterat-omic metallic forces.

Accordingly, it is another object of the invention to provide a processfor removing the pores in metallic coatings, the process including therolling of the metal coated strip or other material immediatelyfollowing the deposition of the coating material and prior to theexposure of the coat-ed metal to the atmosphere, whereby the closing ofthe pores is accomplished prior to the formation of oxides on the metalcoatings while the metal is in a nascent state so that the metal of themetal coatings may flow under pressure and the pores therein be weldedshut.

A further object of this invention is to provide a novel process offorming non-porous vacuum metallized coatings, the process including thenormal cleaning and metal coating steps in vacuo, after which the metalcoated strips or other materials are rolled while still within thevacuum and the coating metal is in a nascent state to effect acompressive deformation of the metal coating with the result that thepores thereof are welded shut and the porosity of the metal coating iseliminated.

Still another object of the invention is to provide a novel process forclosing the pores in metallic coatings applied by a gas plating processwhere the metal coating is deposited from a carbonyl, halide or othergaseous compound, the metal coated strip or other material being rolledwithin the gas of the gas plating process prior to exposure to air, sothat the metallic coating is rolled while in its nascent state prior tothe formation of oxides thereon and the flowing of the metal coatinginto pressure contact during the rolling process brings about thewelding shut of the pores therein.

A still further object of the invention is to provide a novel process ofproducing non-porous metallic coatings, the process being of a naturewherein it is adaptable to vacuum coating processes, gas platingprocesses and even to electroplating processes, the process essentiallyincluding the rolling of the metallic coating prior to the exposurethereof to the atmosphere to eliminate the formation of oxides thereonwhereby, when the metallic coating is rolled and the pressures aresufiicient to effect the flowing of the metal of the metallic coatingswith the open pores in the initially deposited metal being closed by theflowing of the metal and being welded closed through the pressureengagement of the metal while in its nascent state.

Yet another object of this invention is to provide a metal coated stripwherein the metal coated strip has been rolled prior to the exposure tothe atmosphere so that the pores thereof have been entirely weldedclosed and the metal coating is of an impervious nature.

A further object of the invention is to provide a novel method ofeliminating pores in a deposited metal coating, the method including therolling of the metal coating while the metal is in its nascent state toeffect the flowing of the metal to completely close the pores and tobring together the atoms of the opposed surfaces of the metal to thenormal interatomic distance for the metal concerned, i.e., about 2(10)"cm., at normal interatomic metallic forces to cause a true joining ofthe metal and a permanent closing of the pores.

With the above and other objects in view that will hereinafter appear,the nature of the invention will be more clearly understood by referenceto the following detailed description, the appended claims, and theillustrated example in the accompanying drawing.

In the drawing:

The figure is a schematic sectional view taken through an apparatus forapplying a metallic coating to strip material by a vacuum depositingprocess and to roll the metallic coating to close the pores thereinprior to the formation of oxides on the surface thereof.

By way of illustrating an embodiment of the invention, the applicationof the invention is schematically illusa trated in the drawing asapplied to a vacuum metallizing process.

For purposes of convenience, and because in most instances the materialbeing coated in accordance with the process of the invention will be inthe form of an elongated strip, the substrate being coated isillustrated as being in the form of a strip S. The strip S, prior to itsarrival to that apparatus illustrated in the drawing, will have passedthrough suitable cleaning means and will have been charged with anexcess amount of hydrogen. The apparatus illustrated in the drawing willinclude an elongated housing, generally referred to by the numeral 10,which housing has the interior thereof at subatmospheric pressures andis divided into a plurality of individual chambers. For descriptivepurposes, the chambers of the housing will be identified here. Thechambers include an entry chamber 11, a heating and cleaning chamber 12,a vapor coating chamber 13, a rolling chamber 14, and an exit chamber15.

The chamber 11 is defined by an end wall 16 or" the housing 10 and apartition wall 17. A vacuum is maintained within the entry chamber 11through a vacuum line 18 which leads to a suitable vacuum pump. Also,the entry chamber 11 is relatively sealed to the atmosphere by means ofa vacuum seal 19 through which the strip S passes in entering into thehousing 10.

The chamber 12 is defined by the partition wall 17 and a partition wall20. The pressure within the chamber 12 will be less than that in theentry chamber 11. Accordingly, the partition wall 17 is provided with avacuum seal 21 through which the strip S passes when passing from theentry chamber 11 into the chamber 12. Heaters 22 are mounted within thechamber 12 to heat the strip S, thus aiding in driving off the storedhydrogen from the strip S, which heat, together with the low pressurewithin the chamber 12, functions to effect a rapid removal of thehydrogen, the hydrogen carrying with it undesirable surface oxides. Thehydrogen is removed from the chamber 12, and the necessary vacuummaintained therein by means of a vacuum line 23 which leads to asuitable vacuum pump.

Still another vacuum line 24 leads from the vapor coating chamber 13.The pressure within the vapor coating chamber 13 is lower still thanthat within the chamber 12, a very low pressure being maintained Withinthe chamber 13 to bring about the desired vacuum depositing of metalvapor on the strip S. Because of the differential in pressures betweenthe chambers 10 and 155, the partition wall is provided with a vacuumseal 25. The chamber 13 is defined by the partition wall 20 and anotherpartition wall 26.

The vapor coating chamber 13 is provided with a plurality of sources ofmetallic vapor, the individual sources being schematically illustratedand being referred to by the numeral 27. It is to be understood that thesources may vary and for the purpose of the present invention, thenature of the vapor sources is immaterial.

The rolling chamber 14 is defined by the partition wall 26 and apartition wall 28. A vacuum is maintained within the rolling chamber 14by means of a vacuum line 29 which leads to a suitable vacuum pump. Thepressure within the rolling chamber 14 may be greater than that Withinthe vapor coating chamber 13, or the chamber 14 may be sealed relativeto the chamber 13 solely to exclude the coating metal vapor therefrom.Accordingly, the partition wall 26 is provided with a vacuum seal 39 onthe exit face thereof.

When the strip S passes into the rolling chamber 14, it will have thedesired metal coating deposited thereon. Since the rolling chamber 14 ismaintained at a low pressure, it will be seen that the newly coatedstrip S is not exposed to the atmosphere, and therefore a non-oxidizingcondition is maintained and the formation of oxides on the surface ofthe metal coating of the strip S is prevented, the metal coating beingin a nascent state. At this time, it is proposed to roll the metalcoating so as to bring about a flowing thereof with the metal flowinginto the pores therein and pressure welding the pores shut. To this end,a pair of rollers 31 are mounted within the rolling chamber 14 above andbelow the path of the strip S. The rolls 31 are preferably of arelatively small diameter so that the rolls will deflect and therebyconform to the steel substrate or strip S. The diameters of the rollsand the material used in forming the rolls, as well as the unsupportedlengths of the rolls will, of course, all have to be taken intoconsideration. It is, however, necessary that the rolls 31 closelyfollow the surface of the substrate and the metal coating since in a 36inch wide strip, the substrate thickness may vary as much as 00005 inchand the thickness of the metal coating may be only 0.000010 inch to0.00006 inch thick. It is also desirable to use polished rolls because asmooth attractive finish is required. The pressures exerted by the rolls31 on the metallic coating will depend upon the particular metalutilized for the coating metal. However, the pressure must be sumcientto deform the coating metal plastically, thus requiring unit pressuresabove the yield point of the coating metal.

After the metal coated strip S has had the coating metal thereof rolledto close the pores, the strip S passes through a vacuum seal 32 carriedby the partition wall 28 into the exit chamber 15. The exit chamber 15is defined by the partition wall 28 and an end Wall 33 of the housing10. A vacuum is maintained within the exit chamber 15, but the pressurewithin the exit chamber 15 is higher than that within the rollingchamber 14, thus necessitating the vacuum seal 32. The vacuum within theexit chamber 15 is maintained by a vacuum line 34 which is connected toa suitable vacuum pump. Since the coated strip S passes from the exitchamber 15 into the atmosphere, the end wall 33 is also provided with avacuum seal 35 through which the strip S passes.

In the vacuum metallizing of the strip S, the most common coating metalused will be aluminum. However, the invention is not restricted toaluminum in that many other coating metals, including nickel, titanium,etc., may be utilized. In accordance with this invention, it is onlynecessary that the coating metal be somewhat softer than the substratemetal in order that the coating metal will deform during the rollingprocess as opposed to the deformation of the substrate metal, althoughsome deformation of the substrate metal may occur.

The rolling of the coating metal while it is still in its nascent stateand free of oxides or chemi-sorbed oxygen produces a pore closing resultnot otherwise possible. As previously mentioned, when porous metal isrolled after being subjected to oxide forming conditions, althoughsufficient pressures may be exerted on the metal coating to effect theflowing of the metal into the pores, the pores are not completelyclosed. As a result, in the case of a coated steel substrate, forexample, rusting of the steel substrate will occur in a relatively shorttime when the coated steel substrate is subjected to a warm humidatmosphere. This is primarily due to the tendency of the metal to springback when the rolling pressure is released with the resultant separationof metal surfaces which were in contact when the metal was under thepressure conditions imposed thereon during the rolling operation. Gn theother hand, when the atoms of two metal surfaces are in a nascent stateand are brought together within the normal interatomic distance for themetal, i.e., generally 2(10) cm., at normal interatomic metallic forces,there is a true joining of the metal. Under the conditions of thepresent invention, the newly applied metal coating, the coating metal ismaintained in a nonoxidizing condition until it has passed between thepressure applying rolls and as it passes through the pressure applyingrolls, the metal is caused to flow to fill the naturally occurringpores. The surfaces of the metal coating that come into contact as thepores are closed are still in a nascent state and when sufficientpressure is applied, the surfaces move together to the normalinteratomic distance for the metal, i.e., generally 2(l0)' cm., atnormal interatomic forces to effect a true joining of the abuttingsurfaces. This joining or welding of the surfaces prevents spring backand thus results in a complete closing of the pores. Oxidation of thesubstrate metal cannot take place in the absence of the pores andrusting of the substrate metal is eliminated.

The application of this invention to a gas plating process has not beenillustrated. It is to be understood, however, that the coated strip willpass from the gas plating chamber into a rolling chamber without beingexposed to the atmosphere. Also, it is to be understood that the rollingchamber will be filled with the gas utilized in the gas plating process.Thus, the formation of oxides on the surface of the newly depositedcoating metal prior to rolling will be prevented.

The present invention will also apply to electroplated coatings.However, with electroplated coatings, the coated strips must be rolledwithin the electrolyte and there is the problem of the electrolyte beingtrapped within the pores.

From the foregoing, it will be seen that novel and advantageousprovision has been made for carrying out the desired end. However,attention i again directed to the fact that variations may be made inthe example methods and apparatus disclosed herein without departingfrom the spirit and scope of the invention as defined in the appendedclaims.

I claim:

1. A process of forming a non-porous metal coating on a substratecomprising the steps of vacuum depositing a porous metal coating on thesubstrate with the coating metal being somewhat softer than thesubstrate, and roll ing the metal coated substrate to close the pores inthe metal coating while maintaining the metal coating in a non-oxidizingcondition at all times between the depositing step and the rolling step.

2. A process of forming a non-porous metal coating on a strip substratecomprising the steps of vacuum depositing a porous metal coating on thesubstrate with the coating metal being somewhat softer than thesubstrate, and rolling the metal coating while continuously maintainingthe metal coating within a non-oxidizing atmosphere during and betweenall of the steps.

3. A process of forming a non-porous metal coating on a substratecomprising the steps of vacuum depositing a porous metal coating on thesubstrate with the coating I metal being somewhat softer than thesubstrate, and rolling the metal coated substrate to close the pores inthe metal coating while continuously maintaining the metal coatingwithin a vacuum during and between all of the steps.

4. The process of claim 3 wherein the metal coating is made plasticduring the rolling thereof and the metal of the metal coating flows intothe pores.

5. A process of forming a non-porous metal coating on a metal substratecomprising the steps of vacuum depositing a porous metal coating on themetal substrate with the coating metal being somewhat softer than thesubstrate, and rolling the metal coated metal substrate to close thepores in the metal coating while continuously maintaining the metalcoating within a vacuum during and between all of the steps.

6. The process of claim 5 wherein the metal of the metal substrate issteel.

7. The process of claim 5 wherein the metal of the metal coating isaluminum.

8. The process of claim 5 wherein the metal of the metal substrate issteel, and the metal of the metal coating is aluminum.

9. A process of forming a non-porous metal coating on a metal substratecomprising the steps of depositing a metal coating on the metalsubstrate from a metal bearing gaseous compound with the coating metalbeing some what softer than the substrate, and rolling the metal coatedsubstrate to close the pores in the metal coating while continuouslymaintaining the metal coating in a non-oxidizing condition during andbetween all of the steps.

10. The process of claim 9 wherein the metal coating is maintained inthe non-oxidizing condition by being passed through an atmosphere of thegaseous compound.

11. A process of forming a non-porous metal coating on a substratecomprising the steps of electro-depositing a metal coating on thesubstrate within an electrolyte with the coating metal being somewhatsofter than the substrate, and rolling the metal coated substrate toclose the pores in the metal coating while maintaining the metal coatingwithin the electrolyte.

12. A method of completely closing the pores in a metal layer comprisingthe steps of providing a metal layer in a nascent state and while insaid nascent state exerting a pressure on said metal to efiect the flowof the metal and the closing of the pores thereof by bringing the metaldefining said pores together to normal interatornic distances for themetal at normal interatomic pressures to cause a true joining.

13. A method of completely closing the pores in a metal layer comprisingthe steps of depositing the metal under non-oxidizing conditions to forma metal layer so as to be in a nascent state and while in said nascentstate exerting a pressure on said metal to efiect the flow of the metaland the closing of the pores thereof by bringing the metal defining saidpores together to normal interatomic distances for the metal at normalinteratomic pressures to cause a true joining.

14. A process of forming a non-porous metal coating on a substratecomprising the steps of depositing a porous metal coating on thesubstrate under non-oxidizing conditions with the coating metal being ina nascent state and somewhat softer than the substrate, and whilemaintaining said coating metal in said nascent state rolling the metalcoated substrate to effect the flow of the metal and the closing of thepores thereof by bringing the metal defining said pores together tonormal interatomic distances for the metal at normal interatornicpressures to cause a true joining.

15. A process of forming a non-porous metal coating on a substratecomprising the steps of depositing a porous metal coating on thesubstrate within a vacuum to maintain the nascent state of the coatingmetal as it is deposited with the coating metal being somewhat softerthan the substrate, and rolling the metal coated substrate whileretaining the metal coated substrate within a vacuum to maintain thenascent state of the coating metal and to effect the flow of the metaland the closing of the pores thereof by bringing the metal defining saidpores together to normal interatomic distances for the metal at normalinteratomic pressures to cause a true joining.

16. The process of claim 15 wherein the metal of the metal substrate issteel, and the metal of the metal coating is aluminum.

References Cited by the Examiner UNITED STATES PATENTS 1,823,869 9/31Baur 29-528 2,196,002 4/40 Whitney et a1. 29-528 2,686,355 8/54 Lundin29-528 2,708,304 5/55 Lundin 29-196.2 2,715,259 8/55 Mohler 29196.22,797,476 7/57 Sendzimir 29-528 2,812,270 11/57 Alexander.

2,934,478 4/60 Schickner 204--14.l X 3,066,042 ll/62 Ogden 1'l765.2

WHITMORE A. WILTZ, Primary Examiner.

HYLAND BIZOT, Examiner.

1. A PROCESS OF FORMING A NON-POROUS METAL COATING ON A SUBSTRATECOMPRISING THE STEPS OF VACUUM DEPOSITING A POROUS METAL COATING ON THESUBSTRATE WITH THE COATING METAL BEING SOMEWHAT SOFTER THAN THESUBSTRATE, AND ROLLING THE METAL COATED SUBSTRATE TO CLOSE THE PORES INTHE METAL COATING WHILE MAINTAINING THE METAL COATING IN A NON-OXIDIZINGCONDITION AT ALL TIMES BETWEEN THE DEPOSITING STEP AND THE ROLLING STEP.